It is known to arrange road toll facilities for automatic fee debiting, see for example U.S. Pat. No. 4,303,904 (Chasek) and U.S. Pat. No. 5,144,553 (Hassett et al), incorporated herein by reference.
Such systems to which the present invention refers, presuppose that the majority of vehicles that pass the road toll facility, are provided with a receiver-transmitter unit for radiowaves, such as microwaves. The road toll facility comprises an arrangement by which communication by radiowaves can take place with passing vehicles. This arrangement comprises a transmitter and receiver unit, or a transceiver, for the radiowaves by means of which equipment payment and debiting operations can be carried out for the passing vehicles provided with said receiver and transmitter unit. The transmitter receiver unit usually has the form of a transponder. For this technique compare U.S. Pat. No. 4,075,632 and U.S. Pat. No. 4,242,661, for example, incorporated herein by reference.
However, it may occur that vehicles which are not provided with any receiver and transmitter equipment pass through the toll facility and, therefore, cannot be identified by means of the radiowaves. For identification of such vehicles, if these attempt at passing the toll facility without paying toll, the toll arrangement is provided with camera devices for image registration of the number plates of the vehicles in question for search and post-debiting.
The most advanced system for road tolls of this kind should be adapted to a great flow of traffic in free formation. In such an arrangement, it should be possible for the vehicle to travel a certain distance from the time when a registration has been possible to determine whether the vehicle is identifiable through radiowaves or not, and until the recording operation regarding the number plate has been concluded.
During this displacement, a separation must be maintained in such vehicles for which search and post-debiting shall take place, and such for which payment is to be secured by means of the radio communication. This requires additionally that the toll arrangement is also provided with equipment for positioning detection when the vehicles travels in free flow without determined lanes. A known way to detect the position of a vehicle or other body is to process reflected radiowaves which have been received by two or more antennae. By successive position detection of moving vehicle it is possible to track the same. Such a tracking system is known from CA,C,2,100,723 (O'Connor et al.).
In the present connection the transponder of the vehicle equipment functions as reflecting means to accomplish the position detection. Thereby the position of the vehicle is, during its movement, successively measured against a transponder in the vehicle by means of the position detection transmitter-receiver equipment, which in each unit has at least two receiver elements. The phase position in the signal received from the various elements are compared, by which the direction and position of the vehicle can be calculated. This position determination is consequently related to the transponder of the vehicle.